In a concentrating solar power plant of the tower type, solar radiation is reflected by a series of mirrors, called heliostats, toward a central solar receiver situated on a tower, which transfers the energy from the solar radiation to a heat-transfer fluid that will heat up and hence be usable to produce power.
The heliostats are provided with two rotation mechanisms allowing to track the sun and to always return the solar flux toward a given point, irrespective of the time of day and season.
The solar receiver is installed at the apex of a tower so as to receive solar radiation from all the heliostats with no heliostat hindering the reflection of the flux coming from an adjacent heliostat.
The hot fluid that is generated in the solar receiver may for example be high-pressure and high-temperature steam generated from feed water. The steam can then be directly used in a steam turbine driving a power generator.
The hot fluid may also be a mixture of salts used as a heat fluid that can be stored on the ground in large quantities and used in parallel to the production of steam and the generation of electric power. It is therefore possible to separate the collection of solar energy and the production of power.
The solar receiver installed at the apex of the tower may be of the cavity type or of the external type. In the first case, the cavities are provided on their inside with tube panels, capturing the solar rays, and the effect of the cavity is to reduce radiation losses. In the case of the external type, the tube panels capturing solar radiation are installed outside and all around the tower. Losses are slightly greater relative to the cavity system, but it is easier to concentrate the solar radiation therein, the average thermal flux being significantly higher and the surface of the panels being greatly reduced for a same power.
In the external solution, the planar panels are juxtaposed to form a straight prism with a regular polygonal base. Depending on the installed powers, the polygonal base may have a variable number of faces, for example from 4 to 32.
Common practice is to fasten each of the panels to a stationary structure. Each of the panels can then freely expand under the effect of the temperature increase following the capture of the solar energy.
Document U.S. 2012/312296 discloses a solar boiler comprising a boiler support defining an axis along an inboard-outboard direction. A hanger rod or vertical connecting rod is rotatably mounted to the boiler support. A bracket is mounted rotatably to the hanger rod and a solar boiler panel is mounted to the bracket. The panel of the solar boiler defines a longitudinal axis that is substantially perpendicular to the axis of the boiler support. The hanger rod connects the boiler support to the bracket in order to support the weight of the panel of the solar boiler from the boiler support. The hanger rod and the bracket are configured and adapted to maintain a substantially constant orientation of the bracket during the inward and outward movement of the bracket relative to the boiler support. Indeed, according to one illustrated embodiment, two vertical connecting rods that are parallel to each other form a parallelogram link with the boiler support and the bracket. The connecting rods serve to support the weight of the panel. The latter deforms under the effect of thermal expansion or contraction of the solar panel, but the upward movement of bracket under the effect of the rotation of the connecting rods is negligible. As a result, the solar panel moves practically parallel to itself. The solar panels are not connected to each other. The wind forces are reacted by a shock absorber connecting the bracket to the structure. It is not mentioned that the solar panels can be connected to each other.
Document EP 1 243 872 discloses a solar collector with a plurality of absorbing bodies that absorb solar radiation. These absorbing bodies are porous and allow the passage of aspirated air. The support structure for the solar receivers is formed by modules that have a front wall, a back wall, side walls and a cavity. Tubes pass through each module, those tubes conveying hot air into a collector. Cool air flows countercurrent through cool-air inlets in the cavity. The cool air flows around the absorbing bodies. Since they are cooled, the modules may be made from steel without any risk of overheating. The solar receiver is stable and does not require a stop device in the hot air enclosure. The different modules are mounted adjacent to connecting elements, so that they can withstand thermal expansion without tension. Also, the adjacent sides of the modules do not touch over their entire surface, and corner-shaped gaps are provided to that end. Furthermore, the various vertically-mounted modules are connected by their upper portion to the inner wall by an articulated link, which allows expansion in the vertical direction.
Document WO 2013/019670 describes a modular solar receiver, having multiple tube panels in a rectangular, square, polygonal or circular configuration and designed to be used with fused salt or with another heat-transfer fluid. The heat-transfer fluid flows along a vertical path winding through the sides (facets) of the solar receiver. The solar receiver may be assembled in the warehouse and may be used with a support tower to form a solar power system.
Document WO 2010/048578 discloses a heat exchanger with solar receiver assembled in the warehouse and having an arrangement of heat-transfer surfaces and a vertical steam/water separator that is structurally and fluidically interconnected thereto. A vertical support structure is provided to support the vertical separator and the heat-transfer surfaces. The vertical support structure is supported from underneath, while the vertical steam/water separator and the heat-transfer surfaces of the heat exchanger are supported from above from the vertical support structure. The vertical support structure provides structural support and rigidity for the heat exchanger and a means by which the heat exchanger can be grasped and lifted to be placed at a desired location.
In the latter two installations, horizontal reinforcing ribs or beams are attached to the solar tube panels. All the panels are supported from above and suspended from the support structure inside the receiver. Each tube panel comprises two interconnecting plates. Each plate is connected by two bars, pivoting at their ends using pins, to a tab that is attached to a flexion support that in turn is attached by structural steel to the columns comprising the vertical support structure of the receiver. The pivoting bars allow a certain rotation of the solar panels and therefore allow to react the average thermal expansion of the supported panels. This system provides horizontal stability to the tube panels while allowing the tubes a free and independent vertical extension, with reduced tension on the tubes. Here also, the adjacent tube panels, on each face and at each level (top/bottom), are laterally (horizontally) separated from one another, which allows differential expansion of the tube panels, without tension.
Document EP 0 106 688 discloses a receiver for receiving solar radiation energy, characterized by a plurality of steam generating tube panels suitable to receive a flow of liquid to be heated and to produce steam, and a plurality of superheating tube panels suitable to receive a flow of steam to be superheated, the steam generating tube panels and the superheating tube panels being positioned in a side-by-side relationship to receive the solar radiation energy, and the superheating tube panels being intercalated with the steam generating tube panels according to a sequence of at least twelve panels, such that each sequence of four panels among at least twelve panels comprises at least one superheating tube panel and at least one steam generating tube panel. The problem here arises from the fact that the superheating tube panels undergo a much greater longitudinal expansion than the steam generating tube panels. Similarly to the preceding case, the superheating tube panels are connected by connecting rods to horizontal reinforcing ribs. This system allows the superheating tube panels to move vertically relative to the horizontal ribs, and therefore relative to the steam generating tube panels.